Local labs are working to develop treatments for neurological disorders, multiple forms of cancer, and dozens of rare genetic diseases. But the next potential blockbuster drug to emerge from the Boston area may target a less fearsome condition that nonetheless afflicts 30 million to 40 million Americans: irritable bowel syndrome. Within the next few weeks, the Food and Drug Administration will decide whether an experimental drug called linaclotide can be approved for sale in the United States. If the FDA signs off on it, the drug would bring a new treatment option to people suffering from abdominal pain, bloating, and eating limitations as a result of irritable bowel syndrome — known as IBS — as well as chronic constipation. It would also catapult linaclotide’s maker, 14-year-old Ironwood Pharmaceuticals Inc., into the elite club of the area’s commercial drug companies.